A major problem in a synchronous data network is preventing data overflow in a node in which data is being received faster than it is being transmitted. Receive and transmit data rates in a node differ if there is a difference in frequency between the receive clock and the transmit clock. This frequency difference occurs if the transmit data rate is dependent on the node's transmit clock and the receive data rate is dependent on the adjacent node's transmit clock.
One method for preventing overflow is to synchronize the transmit clock and the receive clock. One such clock synchronization method is described in U.S. Pat. No. 5,896,427 issued on Apr. 20, 1999 entitled “System and Method for Maintaining Network Synchronization Utilizing Digital Phase Comparison Techniques with Synchronous Residual Time Stamps” by Muntz et al. This method requires synchronizing on a per bit basis which is complex and expensive and can not be used on all data networks.
Another method for preventing data overflow is to provide a large buffer in the node. The disadvantages of this method are that the buffer adds delay to the transfer of data through the node, the addition of a buffer to the node increases the cost of the node and the buffer cannot prevent overflow if the buffer is not large enough.
Yet another method for preventing data overflow is to implement flow control in the node. Flow control requires large buffers which add delay through the node. Also, flow control can not be used in all data networks, such as wide area networks.